Apoptosis, or programmed cell death, is a highly ordered, genetically controlled process which plays a vital role in both healthy and disease states, including embryogenesis, tissue homeostasis and remodeling, cancer, autoimmune disorders, viral infections, and certain degenerative disorders.
The death domain of TNF receptor-1 (TNFR1) triggers distinct signaling pathways leading to apoptosis and activation of the NF-κB transcription factor through its interaction with the C-terminal death domain of TRADD, a 34 κDa cytoplasmic protein [see Hsu et al., Immunity 4:387-96 (1996)]. TRADD interacts strongly with RIP (receptor-interacting protein; Stanger et al., Cell 81:513-23 (1995), a 74 κDa serine-threonine kinase that with a C-terminal death domain involved in apoptosis; RIP also activates NF-κB. A second RIP protein, RIP2 or RICK [see McCarthy et al., J. Biol. Chem. 273:16968 (1998) and Inohara et al., J. Biol. Chem. 273:12296 (1998)] also contains a death domain and activates NF-κB.
A characteristic feature of apoptosis is activation of a cascade of cytoplasmic proteases that results in the cleavage of selected target proteins. ICE (interleukin 1 beta-converting enzyme) family proteases, also known as caspase proteases, initiate the active phase of apoptosis by degrading specific structural, regulatory, and DNA repair proteins within the target cell [Lazebnik et al., Nature 371:346-7 (1994); Casciola-Rosen et al., J. Biol. Chem. 269:30757-60 (1994)]. For example, a RIP-like kinase, termed CARDIAK/RICK or RIP2 [see Thome et al., Current Biol. 8:885-88 (1998); McCarthy et al., J. Biol. Chem. 273:16968-75 (1998); Inohara et al., J. Biol. Chem. 273:12296-300 (1998)] has been shown to associate with caspase-1. These caspases are related to the C. elegans cell death gene product. Caspases are cysteine proteases that display aspartate specificity, and have been shown by a number of researchers to be crucial to apoptotic pathways. For a review, see Cryns et al., Genes & Development 12:1551-70 (1998). The natural substrates of the caspases are key regulatory and structural proteins, including protein kinases and proteins involved in DNA repair and cytoskeletal integrity.
There are a number of inhibitors of apoptosis (IAPs) that have been identified. Originally identified in baculoviruses, IAPs suppress the host cell death response, thereby allowing survival and propagation of the virus. To date, there are five human IAPs identified, which when expressed in human cells can inhibit apoptosis induced by a variety of stimuli. In addition, the IAPs have been shown to be fairly selective, with different pathways and/or enzymes being inhibited. Human XIAP, cIAP1 and cIAP2 are direct inhibitors of at least two caspase family members, caspase-3 and caspase-7.
Accordingly, the proteins involved in apoptosis and its regulation are of paramount interest, and it is an object of the invention to provide novel apoptosis proteins, herein termed Apop proteins, and in particular Apop1, Apop2, and Apop3 proteins and related molecules. It is a further object of the invention to provide recombinant nucleic acids encoding Apop proteins, and expression vectors and host cells containing the nucleic acid encoding them. A further object of the invention is to provide methods for screening for antagonists and agonists of Apop proteins.